Add option to Proxy factories to copy parameter-level annotations [SPR-8560]

[spring-projects-issues]

Paul Benedict opened SPR-8560 and commented

When using proxies from Spring AOP, it is not possible to examine the intercepted method for ElementType.PARAMETER annotations. My best solution so far, which wastes cycles, is to unwrap the spring proxy, lookup the actual method on the target source with the same call signature and then examine that for annotations.

Spring could easily provide a better way if it allowed these annotations to be copied onto the proxy method.

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Affects: 3.0 GA

Issue Links:

• Add support in AopUtils for obtaining target class transitively when target is an AopProxy [SPR-7074] #11734 Add support in AopUtils for obtaining target class transitively when target is an AopProxy

[spring-projects-issues]

Chris Beams commented

Hi Paul,

Perhaps you could expand on what you mean by 'copying annotations to the proxied method'? Aside from manipulating the bytecoded of the generated proxy directly, there's not really a straightforward way to do this that I'm aware of.

Alternitavely, we could consider providing a utility method (within AopUtils, for example) that performs this kind of unwrap-and-extract behavior.

It might help as well if you could explain your particular use case a bit further.

[spring-projects-issues]

Paul Benedict commented

First, I would like to say that I think the closest code in Spring that unwraps a proxy is AopProxyUtils#ultimateTargetClass()... except it returns the ultimate target class, not the target object. I find that kind of funny because you have to get to the object to determine the class. Perhaps if you added #ultimateTargetObject(), that would meet my needs.

However, I think the proxies "need" more information on them in general. Particularly, the ElementType.METHOD and ElementType.PARAMETER annotations copied from the target. My use case is to perform certain validation on method parameters if a particular PARAMETER annotation is present. As I said, I unwrapped the proxy (one level deep), and then lookedup the method on the target that had the same method signature. This satisfied my use case, but it's too much code. I think a proxy in general should look identical to the target method, including its annotations.

I'll at least take new methods like #ultimateTargetObject() and #ultimateTargetMethod() to make life easier.

[spring-projects-issues]

Chris Beams commented

Juergen, you added ultimateTargetClass in response to #11734, but mentioned there possible side effects with accessing non-singleton TargetSources, which makes sense. Perhaps you could review the request here and see about adding an ultimateTargetObject method? It seems reasonable to provide this with the caveat that it is only suitable for singleton-scoped sources.

Paul, it would be useful if you could paste in your own routine for unwrapping targets just to make sure that we're providing something compatible.

[spring-projects-issues]

Paul Benedict commented

I used the method given in this post:
http://forum.springsource.org/showthread.php?60216-Need-to-unwrap-a-proxy-to-get-the-object-being-proxied&highlight=bean+instanceof+Advised

[spring-projects-issues]

dheerja arora commented

Hi Paul
Is this resolved?

[spring-projects-issues]

Bulk closing outdated, unresolved issues. Please, reopen if still relevant.